In tea leaves, the same green leaf is processed into green tea, black tea, oolong tea, etc. by controlling biological oxidation, a process also incorrectly called fermentation.

This process is more like a series of enzymatic reactions, perhaps better known as biological oxidation. The biooxidation of tea is a series of oxidation processes of catechins that are promoted by oxidase in the cell wall after the cell wall is damaged.

In the cells of tea, catechins are present in the cell fluid, and oxidase is mainly present in the cell wall, not mainly in microorganisms, so the cell wall needs to be damaged. This also naturally explains why fermented tea needs to be kneaded. According to the degree of oxidation of polyphenols, it is also divided into full fermentation, semi-fermentation and light fermentation.

In black tea, the degree of oxidation of polyphenols is very high, which is called full fermentation; the degree of oxidation of polyphenols in oolong tea is about half, which is called semi-fermentation.

For example, in black tea processing, the purpose of fermentation is to oxidize the catechins contained in the leaves. The leaf color changes from green to copper red, resulting in the unique color of black tea. After the tea liquid cell membrane is damaged, the polyphenols, amino acids and other substances in the vacuole are gradually oxidized. At the same time, due to the oxidation of catechins, some substances in the leaves undergo chemical action, resulting in the unique color, aroma and quality of black tea.

The above is the basic meaning of fermentation in Chinese tea.

Due to the variety of tea in China, the processing techniques and production methods are rich and colorful, and the definition of quality formation is different. In the production and quality formation process of some teas, in addition to the above-mentioned fermentation in the sense of biooxidation in addition to its own enzymatic reaction, In some links, microorganisms will also participate.

For example, in addition to the enzymatic effect, microorganisms are also involved in the stacking fermentation process of cooked Pu-erh tea.

After separation and research, the main microorganisms are Aspergillus niger, Aspergillus oryzae, Aspergillus claudin, Aspergillus griseus, Rhizopus, lactic acid bacteria and yeast. Nonetheless, it is still necessary for us to clearly distinguish fermentation involving microorganisms from fermentation in the sense of biooxidation. Otherwise, the conceptual ambiguity will easily lead to misinterpretation of the mechanism of tea quality formation.